This invention relates to magnetic work-holding devices and is more particularly concerned with an improved permanent magnetic chuck assembly.
Various types of permanent magnetic chucks are known in the art.
Churchill U.S. Pat. No. 3,109,967 describes a magnetic chuck in which an inner member having a plurality of permanent magnets is slidably movable from a position in which the magnets energize magnetizable bars in the workpiece receiving surface to a position in which the magnets are in contact with non-magnetizable bars in the same surface.
Engelsted U.S. Pat. No. 3,231,789 describes a chuck in which there is a fixed member having a plurality of plate-shaped permanent magnets and of plate-shaped soft magnetic bodies separating the magnets and a laterally movable member having a corresponding array of magnets and magnetic bodies. In each member the magnets have alternating polarity. In the ON position of the chuck the magnets in the fixed and movable members have like polarity. In the OFF position the magnets in the two members have opposite polarity thus producing a weakened magnetic field. Uchikune et al U.S. Pat. No. 4,408,752 shows a related device.
Magnetic chucks have also become known in which rotary switch mechanisms are employed. Wesemann U.S. Pat. No. 2,203,512 describes a chuck in which a long bar permanent magnet can be rotated from a position in which it energizes a pole bar in the workpiece receiving surface to a position in which polarity is reversed.
Bing et al U.S. Pat. No. 2,209,558 employs bipolar cylindrical magnets rotatable within sleeves of soft iron which form the workpiece receiving surface. Beechlyn U.S. Pat. No. 2,347,023 employs a rotatable bar magnet centered between two permanent magnets located in the magnetizable body of the chuck. In the ON position the field of the rotatable magnet reinforces that of the permanent magnets. In the OFF position the fields are opposed. Lee U.S. Pat. No. 4,900,888 describes a chuck comprising upper and lower magnetizable plates separated by an insulating layer with a cylindrical bipolar magnet mounted rotatably and longitudinally separating the insulating layer into two parts. In the ON position one pole of the cylindrical magnet is in contact with the upper plate and the other with the lower plate. In the OFF position both poles contact each plate.
The present invention represents a significantly improved magnetic chuck assembly having greater holding power and characterized by simplified construction which makes the manufacture of the device significantly easier.